| package org.apache.lucene.store; |
| |
| /* ==================================================================== |
| * The Apache Software License, Version 1.1 |
| * |
| * Copyright (c) 2001 The Apache Software Foundation. All rights |
| * reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * |
| * 3. The end-user documentation included with the redistribution, |
| * if any, must include the following acknowledgment: |
| * "This product includes software developed by the |
| * Apache Software Foundation (http://www.apache.org/)." |
| * Alternately, this acknowledgment may appear in the software itself, |
| * if and wherever such third-party acknowledgments normally appear. |
| * |
| * 4. The names "Apache" and "Apache Software Foundation" and |
| * "Apache Lucene" must not be used to endorse or promote products |
| * derived from this software without prior written permission. For |
| * written permission, please contact apache@apache.org. |
| * |
| * 5. Products derived from this software may not be called "Apache", |
| * "Apache Lucene", nor may "Apache" appear in their name, without |
| * prior written permission of the Apache Software Foundation. |
| * |
| * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED |
| * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
| * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE |
| * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR |
| * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF |
| * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND |
| * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, |
| * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT |
| * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| * SUCH DAMAGE. |
| * ==================================================================== |
| * |
| * This software consists of voluntary contributions made by many |
| * individuals on behalf of the Apache Software Foundation. For more |
| * information on the Apache Software Foundation, please see |
| * <http://www.apache.org/>. |
| */ |
| |
| import java.io.IOException; |
| |
| /** An interprocess mutex lock. |
| * <p>Typical use might look like:<pre> |
| * new Lock.With(directory.makeLock("my.lock")) { |
| * public Object doBody() { |
| * <it>... code to execute while locked ...</it> |
| * } |
| * }.run(); |
| * </pre> |
| * |
| * @author Doug Cutting |
| * @see Directory#makeLock(String) |
| */ |
| |
| public abstract class Lock { |
| /** Attempt to obtain exclusive access. |
| * |
| * @return true iff exclusive access is obtained |
| */ |
| public abstract boolean obtain() throws IOException; |
| |
| /** Release exclusive access. */ |
| public abstract void release(); |
| |
| /** Utility class for executing code with exclusive access. */ |
| public abstract static class With { |
| private Lock lock; |
| private int sleepInterval = 1000; |
| private int maxSleeps = 10; |
| |
| /** Constructs an executor that will grab the named lock. */ |
| public With(Lock lock) { |
| this.lock = lock; |
| } |
| |
| /** Code to execute with exclusive access. */ |
| protected abstract Object doBody() throws IOException; |
| |
| /** Calls {@link #doBody} while <it>lock</it> is obtained. Blocks if lock |
| * cannot be obtained immediately. Retries to obtain lock once per second |
| * until it is obtained, or until it has tried ten times. */ |
| public Object run() throws IOException { |
| boolean locked = false; |
| try { |
| locked = lock.obtain(); |
| int sleepCount = 0; |
| while (!locked) { |
| if (++sleepCount == maxSleeps) { |
| throw new IOException("Timed out waiting for: " + lock); |
| } |
| try { |
| Thread.sleep(sleepInterval); |
| } catch (InterruptedException e) { |
| throw new IOException(e.toString()); |
| } |
| locked = lock.obtain(); |
| } |
| |
| return doBody(); |
| |
| } finally { |
| if (locked) |
| lock.release(); |
| } |
| } |
| } |
| |
| } |